In the natural environment, plants often grow under unfavorable conditions, including water deficit conditions such as drought, a severe form of low water availability generally characterized as a prolonged period of water deficit. Water deficit, or water deprivation, can delay growth and development, reduce productivity, and in extreme cases, cause the plant to die. Low water availability is a major factor in crop yield reduction worldwide. Problems for plants caused by low water availability include mechanical stresses caused by the withdrawal of cellular water. Drought also causes plants to become more susceptible to various diseases (Simpson, ed. (1981) “The Value of Physiological Knowledge of Water Stress in Plants”, in Water Stress on Plants, Praeger, NY, pp. 235-265).
A number of polypeptides, including, for example, transcription factors (TFs), have been shown to improve the tolerance of plant species to water deficit conditions (for examples, see publication no. WO2004076638). However, important limitations in the use of various proteins that confer water deficit tolerance to crop species when the proteins are overexpressed may include negative side effects associated with constitutive overexpression of these polypeptides. Possible pleiotropic effects such as small size, delayed growth, increased disease sensitivity, and development and alteration in flowering time are common. It has been proposed that genes conferring tolerance to water deficit impose a cost on overall fitness and development. To overcome these limitations, the present studies were initiated to discover and assess the utility of numerous promoter sequences that respond to water deficit conditions. These promoter sequences can be used to regulate protein expression during periods of drought or other water deficit conditions, and therefore may be used to induce overexpression of polypeptides that can confer improved water deficit tolerance when they are needed without the adverse developmental or morphological effects that may be associated with their constitutive overexpression. Numerous transgenic plants using these promoter sequences to regulate polypeptides were developed and the plants were analyzed for their tolerance to water deficit conditions. Many of these promoter sequences can be used to produce commercially valuable plants and crops as well as the methods for making them and using them.
The present invention thus relates to methods and compositions for producing transgenic plants, where water deficit-inducible overexpression of transcription factors confers enhanced tolerance to water deficit with reduced or no impact on yield, appearance, quality or fitness, as compared to plants constitutively overexpressing the same transcription factors. Other aspects and embodiments of the invention are described below and can be derived from the teachings of this disclosure as a whole.